Heating a restricted area of a packaging material sheet consisting of a thermoplastic with IR light in order to obtain a heated zone for, for instance, deep-drawing of plastic lids, is previously known in this Art.
Within the packaging industry, use is made of continuous material webs for packaging material. This packaging material normally consists of a paper or cardboard layer laminated on both sides with a thermoplastic. The laminate may also include a thin aluminium foil.
After production, the laminate is cut to suitable widths and stored on so-called jumbo reels. In a packaging machine, the packaging material is formed into a tube which is transversely sealed, cut in the transverse seals and finally formed into a finished package. In the majority of cases, it is necessary to protect the inner laminate edge when the packaging material is formed into a tube. This may be effected by sealing a loose thermoplastic strip against the inside of the laminate, alternatively, or by allowing a narrow edge of thermoplastic during, on production of the packaging material, to project out beyond the one laterally defining line of the laminate.
The thermoplastic edge, which may possibly be laminated with adhering aluminium foil, is, in a later process prior to the filling machine, to be folded over the open laminate edge and sealed against the laminate surface of thermoplastic. In this instance, it is necessary to heat the packaging material web before the edge is folded so that sealing of the edge against the laminate surface may take place. In this case, a restricted heating of the continuous material web is desirable. Also in the application of loose plastic strips, a restricted heating of the continuous material web is desirable.
According to prior art technology, the edge of the continuous material web has hitherto been heated, before the folding operation, by hot air. A hot air jet is directed from a hot air nozzle towards the edge of the continuous material web. In this instance, a scattered heating effect is obtained which is difficult to restrict in physical terms. In addition to the laminate edge, the thermoplastic edge is also heated, which results in the thermoplastic edge becoming soft and intractible for handling in a subsequent folding operation. This is particularly true when the thermoplastic edge is laminated with aluminium foil, since heating of the edge may entail crack-formation and creaseformation in the thin aluminium foil, with a resultant edge folding which is not completely gas-tight, which in turn may cause insterility in aseptic packaging. The subsequent folding operation may be effected with a series of rollers of different angles of inclination, or alternatively with a belt which folds over the edge.